Domestic taps typically have an inlet which is adapted for coupling to a water pipe, a bulbous body in which is disposed a valve seat and valve cartridge, and an outlet in the form of a spout through which water can flow. The valve cartridge is provided with a stem having a handle located outside the body at one end and a washer located within the body at an opposite end for sealing against the valve seat. By turning on the handle, the stem is rotated about its longitudinal axis so as to axially move within the tap body. To close the tap, the handle is turned in a first direction so as to screw down the stem and push the washer against the valve seat. To open the tap, the handle is turned in the opposite direction and the washer is displaced upward by fluid pressure to allow water to flow through the valve seat and out the outlet.
The main cause of leakage in such taps is due to wear of the washer. This wear is usually caused by over-tightening of the handle and stem which leads to tearing, cutting or fracturing of the washer. Washers are normally loosely held within the bottom of the stem so that the two can rotate relative to each other. However, when the stem is over-tightened, the washer can also turn with the stem to accelerate wear against the valve seat.